1. Technical Field
This technology pertains generally to magneto-resistance (MR) sensors, and more particularly to magneto-resistance (MR) sensors which may incorporate spin valve or magnetic tunnel junction (MTJ) devices.
2. Background Discussion
Magneto-resistance (MR) sensors based on spin valve and magnetic tunnel junction (MTJ) devices have been widely used in applications such as magnetic field sensors, position and rotation sensors, as well as medical applications because of their large signal, low power consumption, and long endurance.
In magnetic sensors, the central issue is the linear and reversible response to the magnetic field. At present, one popular method is to align the magnetizations of a sensing layer and a reference layer to be initially perpendicular to each other in the plane of the film. This can be obtained by introducing an external or internal transverse bias field, or by utilizing shape anisotropy and step edge anisotropy. However, such designs complicate sensor design, and suffer from magnetization fluctuation and magnetic noise when reducing sensor size. This limits the scalability and integration for applications.
Another approach employs out-of-plane magnetized materials to achieve a linear and hysteresis-free response. For example, linear response and large linear field range have been obtained in sensors with a perpendicularly magnetized reference layer and in-plane sensing layer. A sensor with a high linearity up to applied field of 500 Oe has been demonstrated by using Pt/CoFe out-of-plane magnetized sensing layer. However, multilayer-based structures using transition metals such as Pt- and Pd-multilayer structures exhibit small MR due to their low spin polarization, further resulting in low sensitivity.